Project Summary: While hospitalizations for older patients generally provide a net benefit when appropriate, hospitalizations for older patients also carry significant risks including an irreversible decline in both physical and cognitive functional status, often resulting in loss of quality of life and greater risk of placement in nursing homes. Elderly patients are also at increased risk of in-hospital falls, delirium, medication interactions, nosocomial infections, and medical errors. Thus, while excess use of the hospital affects all age groups, overuse of the hospital has substantially disproportionate consequences for the elderly. To this point there is little empirical data to help characterize the factors associated with admission rates for the elderly or the extent to which the complex social, cognitive, and physical factors common to elderly patients contribute to higher rates of hospitalization for patients who present for care in the Emergency Department (ED). Additionally, factors related to individual emergency physicians (EPs) who typically make the decision whether to admit or not, and the hospitals where patients present for care may further influence the likelihood of admission. Payment changes in health care also may influence rates of hospitalization for elderly patients and are crucial policy levers available to influence admissions. In particular, the recent advent of Accountable Care Organizations (ACOs) with incentives to reduce spending globally and improve quality may differentially reduce admissions. The proposed study will utilize data on Medicare beneficiaries and their care providers to accomplish three key aims. Using nationally representative data from the Medicare program aims 1 and 2 will examine the predictors of and variation in rates of admission of elderly patients from the ED focusing on discretionary conditions. We also will examine whether factors that influence the decision to admit are also associated with adverse outcomes, including mortality and ED revisits. Potential factors will be drawn from our novel conceptual framework and include patient, EP, hospital, and market characteristics. In Aim 2, we will supplement these measures with data from the Health and Retirement Study to examine measures unique to the elderly including functional status, cognition, and social support. Aim 3 will serve as a proof of concept and will evaluate the impact of Medicare's Accountable Care Organization programs, which through systems changes as a response to payment incentives would benefit from reducing potentially discretionary admissions to the hospital. These aims are important and timely and built upon the scientific premise that safely reducing admissions from the ED could ultimately result in improved quality of care, maintenance of independence, reduced mortality, and substantial cost savings.